1. Field of the Invention
This invention is in the field of tools for forming collared holes.
2. Description of the Prior Art
Heat transfer coils include a plurality of coolant tubes typically joined together by brazed joints. A header coolant tube is typically provided with a plurality of openings which lead into a plurality of smaller diameter coolant tubes. It is customary to provide a collar extending around each of the openings in the header conduit with the smaller diameter coolant tubes then extending into each opening being brazed to the collars. It is customary to also braze the collars to the larger diameter header tube. The brazed joint between the collar and the header may eventually fail resulting in a leak through which the coolant may escape. The collars must be separately produced and installed in the header conduit adding considerably to the cost of manufacturing the heat transfer coils.
Disclosed herein is a method and tool for producing a collar integral with the workpiece eliminating the prior requirement or step of brazing the collar to the workpiece. The integral connection between the collar and workpiece eliminates the possibility of leakage between the collar and the workpiece. The collar formed with the tool and method disclosed herein protrudes not only externally from the header tube but also protrudes into the header tube allowing additional area of contact between the collar and the coolant tube inserted therein and brazed to the collar. Another prior method of producing a collared hole includes forming a hole within the workpiece and then projecting a tool through the hole with the tool having expandable flutes or arms which when pulled outwardly through the hole stretches and deforms the material surrounding the hole so as to form an outwardly projecting collar integral with the workpiece.